Problem: $uv - 5uw - 4u + 9 = 8v - 9$ Solve for $u$.
Solution: Combine constant terms on the right. $uv - 5uw - 4u + {9} = 8v - {9}$ $uv - 5uw - 4u = 8v - {18}$ Notice that all the terms on the left-hand side of the equation have $u$ in them. $1{u}v - 5{u}w - 4{u} = 8v - 18$ Factor out the $u$ ${u} \cdot \left( v - 5w - 4 \right) = 8v - 18$ Isolate the $u$ $u \cdot \left( {v - 5w - 4} \right) = 8v - 18$ $u = \dfrac{ 8v - 18 }{ {v - 5w - 4} }$ We can simplify this by multiplying the top and bottom by $-1$. $u= \dfrac{-8v + 18}{-v + 5w + 4}$